Electrocoating compositions are well known and are disclosed in Gilchrist U.S. Pat. Nos. 3,351,675, 3,362,899, 3,575,909 and 3,351,575; in Turpin U.S. Pat. Nos. 4,221,647 and 4,263,194; and in Tsou U.S. Pat. Nos. 4,148,704, 4,155,824 and 4,246,087. Electrocoating compositions are dispersed in dilute water baths and then electrocoated onto cathodic or anodic substrates immersed in the electrocoating bath. The electrocoated films can be heat-cured with catalysts or cured by ultraviolet energy. Cationic electrodeposition coatings have superior durability as compared to anionic electrodeposition coatings.
In cathodic electrodeposition, the conductive metal substrate is the cathode in the electrical process, and an anode is placed in the electrodeposition bath with the electrodeposition coating being incorporated in the aqueous electrolyte between the anode and the cathode. After electrodeposition, the coating compositions must be cured. For example, in Tsou U.S. Pat. No. 4,148,704, the preferred curing is at a temperature ranging from about 250.degree. F. to about 500.degree. F. Air curing by virtue of the high concentration of unsaturated fatty acids is possible, but the corrosion resistance, weather durability and chalking resistance at low temperature curing are not as satisfactory.
Cathodic electrocoating systems that are based on alkaline cationic resins are solubilized or dispersed in water with the aid of an acid.
One of the major problems has been obtaining adequate cure at relatively low temperatures of 150.degree.-175.degree. C. or less. However, the high basicity of the previously known compositions results in poor low temperature cure.
Hazan, in U.S. Pat. No. 4,337,187 provided a hydrophilic polyamine copolymer backbone that wraps around a hydrophobic polyester or alkyd resin which is codispersed with the polyamine copolymer. A substantially neutral pH is thereby provided with a low amount of amine functionality.